1. Field of the Invention
The present invention relates to an upper mounting structure for a strut-type wheel suspension suitably used for suspending a wheel from a vehicle body, which is capable of reducing a transmission of vibration from the wheel to the vehicle body, thereby providing a comfortable ride feeling of a vehicle.
2. Description of the Related Art
Typical examples of conventional upper mounting structure for a strut-type wheel suspension are as shown in FIGS. 1 to 3. The upper mounting structure for a strut-type wheel suspension as shown in FIGS. 1 and 2 is of a so-called isolated input type and the structure as shown in FIG. 3 is of a so-called concentrated input type.
The isolated input type structure in FIG. 1 is disclosed in Japanese Utility Model Application Laid-Open Publication No. 62-25206. In this structure a coil spring 1 is seated at its upper end on a spring support 2 which is coupled with an upper support 4 through a spring insulator 3 of resilient material. The upper support 4 is adapted to be fastened to a vehicle body not shown by a bolt and nut means. The coil spring 1 is directly or resiliently engaged at its lower end to an outer sleeve of a strut assembly 5. A piston rod 6 of the strut assembly 5 freely penetrates through a central opening of the upper support 4 and is secured thereto by means of a pair of rod mounting insulators 7 of resilient material arranged on either side of the upper support 4. On the other hand, the outer sleeve of the strut assembly 5 is resiliently or rigidly coupled with a knuckle not shown which is articulated to a vehicle body or a subframe fixed thereto not shown through a plurality of links.
The isolated input type structure in FIG. 2 is disclosed in SAE Paper No. 901729. In this structure a coil spring 1 is seated at its upper end on a spring insulator 3 of resilient material which is secured to an upper support 4 directly. The upper support 4 is adapted to be fastened to a vehicle body not shown by a bolt and nut means. The coil spring 1 is resiliently engaged at its lower end to an outer sleeve 9 of a strut assembly 5. A piston rod 6 of the strut assembly 5 freely penetrates through a central opening of the upper support 4 and is connected thereto through a rod mounting insulator 10 consisted of a hydraulic mount. On the other hand, an outer sleeve 9 of the strut assembly 5 is resiliently or rigidly coupled with a knuckle not shown which is articulated to a vehicle body or a subframe fixed thereto not shown through a plurality of links.
The concentrated input type structure in FIG. 3 is disclosed in "DATSUN 180SX SERVICE MANUAL, MODEL S110 SERIES" issued by "NISSAN MOTOR CO., LTD." on September, 1979. In this structure a piston rod 6 of a strut assembly 5 is rigidly coupled with a spring support 2 which includes a lower spring support part 2a and an upper spring support part 2b. A coil spring 1 is seated at its upper end on the lower spring support part 2a. The upper spring support part 2b is coupled with an upper support 4 through a strut mounting insulator 11 of resilient material. The upper support 4 is adapted to be fastened to a vehicle body not shown by a bolt and nut means. The coil spring 1 is resiliently or rigidly engaged at its lower end to an outer sleeve of the strut assembly 5. Other constructions of the disclosed upper mounting structure is essentially the same as that of the structure shown in FIG. 1. Now, in FIG. 3, the shown structure is constructed to be useful in a front wheel suspension, so that a bearing 12 is interposed between the lower and upper spring support parts 2a and 2b for easiness of wheel steering.
Each conventional upper mounting structure for a strut-type wheel suspension described above has following problems which will be discussed with respect to FIGS. 4a, 4b and 4c.
FIGS. 4a, 4b and 4c show vibration system models of the structures in FIGS. 1, 2, and 3 respectively. As appreciated from FIG. 4a, the isolated input type structure in FIG. 1 can provide a comfortable ride feeling of a vehicle, since the rod mounting insulator 7 through which the strut assembly 5 is coupled with the vehicle body 14 is made from resilient material of low spring constant both in the longitudinal and transverse directions of the vehicle body 14 in order to successfully avoid that a low frequency vibration input from a road to an unsprung mass 13 of the strut-type wheel suspension may be transmitted to the vehicle body 14 through the strut assembly 5.
In this structure, however, the spring insulator 3 of resilient material has to support a vehicle weight and is designed to have a spring constant more than twice of that of the rod mounting insulator 7, so that when a vertical surge vibration of the coil spring 1 is energized due to vibration input from a road, this surge vibration is transmitted to the vehicle body 14 from an upper end of the coil spring 1 through the spring insulator 3 of large spring constant. This surge vibration is also transmitted to the outer sleeve of the strut assembly 5 through a lower end of the coil spring 1. Well, at high frequency range within which the surge vibration tends to be energize , the piston rod 6 and the outer sleeve of the strut assembly 5 is suppressed to move telescopically to each other because of large oscillation damping effect of the strut assembly 5, so that the above surge vibration is almost directly transmitted to the piston rod 6. This causes a vertical vibration of the strut assembly 5 since the rod mounting insulator 7 is of low spring constant as mentioned above, and then the above vertical vibration of the strut assembly 5 causes the knuckle to be rocked about a center of gravity thereof. This rock motion of the knuckle causes transverse vibration of the vehicle body 14 since the knuckle is articulated to the vehicle body through the plurality of links, and this transverse vibration of the vehicle body 14 together with the above mentioned surge vibration through the spring insulator 3 give rise to compartment noise.
As appreciated from FIG. 4b, the isolated input type structure in FIG. 2 is designed by replacing the rod mounting insulator 7 of resilient material with the hydraulic mount type of rod mounting insulator 10 through which the strut assembly 5 is coupled with the vehicle body 14. In this arrangement the hydraulic mount type of rod mounting insulator 10 is designed to have low spring constant at relative low frequency range except for high frequency range as shown in FIG. 5 for reduction of road noise, so that this arrangement also can not reduce a vibration input due to said surge vibration of the coil spring 1 similarly to the structure in FIG. 1.
On the contrary, in the concentrated input type structure in FIG. 3, as appreciated from FIG. 4c a vibration input from a road to the unsprung mass 13 of the wheel suspension is transmitted to the spring support 2 through the coil spring 1 as well as the strut assembly 5 and the vibration, thereafter, is transmitted to the upper support 4 and the vehicle body 14 through the strut mounting insulator 11, but because of the construction in which the coil spring 1 and the strut assembly 5 are directly coupled with each other in mutual parallel relation, even though surge vibration of the coil spring 1 has occurred, this surge vibration is absorbed as an internal force in closed loop including the coil spring 1 and the strut assembly 5 by the strut assembly 5, and thus the compartment noise due to the surge vibration may be successfully suppressed.
In the described structure, however, the strut mounting insulator 11 of resilient material is designed to have a high spring constant since it must support a vehicle weight by itself, and then the strut assembly 5 is designed to perform a damping effect at a lower frequency range upto the resonance frequency of the unsprung mass 13 for suppressing a resonance of the unsprung mass 13, so that vibration to the vehicle body at the lower frequency range upto said resonance frequency can not be reduced effectively. Also at a higher frequency range, since the strut assembly 5 performs a large damping effect to restrict the relative telescopical movement between the piston rod 6 and the outer sleeve of the strut assembly 5, the majority of a vibration input from a road to the unsprung mass 13 is transmitted to the vehicle body 14 through the strut assembly 5 of large damping effect and the strut mounting insulator 11 of high spring constant. Therefore, the described structure has problems of an uncomfortable ride feeling of a vehicle and a low anti-vibration and noise characteristic over the whole frequency range.